Electronic devices for power supplies or other applications are conventionally provided in a protective, heat-dissipating package. Often, the device (e.g., a metal oxide semiconductor field-effect transistor, or "MOSFET") is attached to a lead-frame by a wire bonding technique. The device is then encapsulated or "molded," wherein an encapsulant is formed about the device to yield a unitary, board-mountable package device. One well-known configuration for board-mountable package is a so-called dual in-line package ("DIP"), wherein electrical leads protrude from opposing sidewalls of the package. The leads are advantageously so arranged to allow the package to be mounted to a circuit board by various conventional soldering processes. DIPs are widely used for packaging integrated circuits, most often in telecommunications or computer-related environments.
In a power electronics environment, the packaged power devices are conventionally mounted directly to a circuit board, using either through-hole or surface-mounting techniques. The devices are then joined with other electronic components to form a circuit, perhaps to function as a power supply such as a DC/DC power converter.
As with other types of electronic components, the trend in the design of power supplies has been toward achieving increased power and device density and lower device profile. However, any improvements in power, density and profile cannot be at the expense of the thermal and electrical characteristics of the components and overall power supply.
Typical power supply assembling techniques commonly include soldering necessary components to a printed wire board (PWB). Necessary components vary from application to application, but usually include power components (commonly a magnetic core) and associated control circuitry. The PWB and components are then encapsulated for mechanical protection and thermal management.
Due to design and market demands, power supplies are now customarily configured to be surface mountable. Problems resulting from such designs include lead coplanarity. Once the supply is finished and reflow soldered, the leads extending from the package need to remain coplanar to ensure proper contact with a larger circuit board.
Further, after the supply is soldered, the package is potted, placing unnecessary stresses upon the components and enclosure as a whole. Once soldered, typical practices include overmolding the entire supply package to further secure the leads. This practice commonly places stresses upon the components and the package as a whole which can cause a number of problems, including, but not limited to magnetostriction. Magnetostriction occurs when power magnetic components suffer compressive stresses during encapsulation. The stresses cause the magnetic properties of the components to degrade to such a point as to be relatively useless.
Another problems encountered involves the solder used in the package during assembly. When the finished package is reflow soldered to a board, the resulting heat commonly causes failures in the earlier soldered components, resulting in failures and reliability problems.
Finally, another problems associated with common assembly techniques centers around the highly manual nature of the process. Numerous labor-filled hours are wasted by hand assembling power supply packages when any type of automation could save abundant amounts of money.
Accordingly, what is needed in the art is a surface mounted power supply that is capable of being fabricated in an automated process while retaining coplanarity and electrical reliability.